A controller transmits output data to an input-output (IO) unit, which outputs signals to devices such as a relay or an actuator connected to the controller via a network. The controller also receives input data from external devices. The controller performs computation using the input data to obtain output data. The controller repeats this series of operations to control machines or devices.
The controller may be connected to one of a plurality of field networks, which are used particularly in the control industry in which real-time response is important.
For example, Patent Literature 1 describes an industrial computer that controls machines via a field network. The industrial computer includes a communication scheduler for controlling communication that is performed cyclically. When receiving a request to transmit data from a program, the communication scheduler temporarily stores the data, and controls the timing to transmit the data using a predetermined timeslot. The communication scheduler thus enables communication in multiple different cycles.